LB and RB boundaries

supposed this is the response ive got to the web server and i want to capture the specific error code what would be my LB and RB(kinda rusty i keep getting No match found for the requested parameter)

":"1","errors":[{"code":"X12345FZ","message":"Unable to process your request

i tried

web_reg_save_param("trial",
                "LB=code":",
                "RB=",
                LAST);